Changes in vision, including total
blindness, sometimes occur after major
surgical procedures.1 In particular, mul-tilevel surgery on the lumbar spine is
known to be associated with visual loss.2
The incidence of POVL ranges from
0.05 percent to 4.5 percent of surgical
cases.3 In comparison, the incidence of
hypoxic-ischemic encephalopathy following birth is 0.2 percent to 0.3 percent,4 and the frequency of misdiagnosed
heart attacks is 1.9 percent.5 POVL is not
only severe; it is also frequent enough
that lawyers should be familiar with it.
The most common cause of POVL is
a decrease in blood and oxygen to the
optic nerve, called ischemic optic neuropathy.6 The duty to maintain adequate
blood circulation and oxygenation during surgery falls on the anesthesiologist.
And while blindness resulting from poor
anesthetic technique is one of the top
patient-safety concerns among anesthesiologists,7 it is not routinely discussed
with patients before surgery.
With long, complicated spine surgeries on the rise, the incidence of this tragic
complication has been increasing.8 If we
are to help patients who have suffered
preventable visual loss from an inappropriate anesthetic technique, we must
understand the physiology involved and
how to defeat expected defense tactics.
Cause and Effect
Many factors interact to cause POVL
from ischemic optic neuropathy. The
more important involve the body’s ability to carry and deliver oxygen to tissues,
particularly the optic nerve, and how this
can be hindered during surgery.
Hematocrit and hemodilution.
Blood carries oxygen from the lungs to
the body tissues using a protein called
hemoglobin in the red blood cells. To
measure the blood’s oxygen-carrying
ability, doctors look at the percentage
of red blood cells present in the bloodstream. This is called the hematocrit.
“It was the
way my face
looked that
most shocked
my wife,
Betty.”
“‘Phil, your face is so swollen,’ she
said tearfully. She was being kind, I
think. I must have been unrecognizable
for her to be so upset. Until then, she had
always been so strong.
“The open sore on my chin stung
each time I touched it. The doctor said
it was caused by pressure from the face
pad during surgery. When I awoke from
back surgery, my eyes were so swollen I
couldn’t open them, so I couldn’t see my
face even if I wanted to. When the doctor
was able to check my vision, all I could
see was bright light.
“‘What happened to me, doc?’ I
asked. The surgery was on my spine,
not on my eyes.
“Looking back, I was scared to death.
My 22 years as a police officer was what
gave me the strength to keep myself
together during that time. They said
there was nothing they could do.
“My vision never got much better,
although with one eye I can now make
out large shadows. The doctors never
did tell me what really happened.”
That is a true story, told by one of
our clients. His injury could have been
prevented; he suffered postoperative
visual loss (POVL) because his anesthesiologist failed to maintain his blood
pressure and blood status during a long
spinal surgery.
Normal hematocrit is 50 percent.
When the hematocrit is lower than
normal—a condition called anemia—the
blood’s oxygen-carrying capability is low,
making the bodily tissues at risk for damage due to an inadequate oxygen supply.
When the patient loses a large amount
of blood during a long surgical procedure,
nonblood fluids are used to maintain the
patient’s blood pressure. The blood is
diluted (called hemodilution), the hematocrit goes down, and the blood’s oxygen-carrying ability is reduced.
Blood and tissue pressure. The
heart pushes the blood through the circulatory system, creating arterial blood
pressure in the process. This pressure
pushes blood into the tissues. When the
arterial blood pressure is reduced, the
heart’s ability to push oxygen-enriched
blood into the tissues is reduced.
The tissues also have pressure and
push back against the blood pressure.
Increased tissue pressure inhibits the
blood’s ability to get oxygen into the tissues. This occurs when the tissues are
swollen, and especially when the swollen tissues are within a confined space,
like the spine’s bony canal.
The venous blood returning to the
heart from the tissues has pressure as
well. When venous pressure is increased,
blood flow out of the tissues is reduced,
and the oxygen-rich blood from the arterial side has difficulty getting in. So, for
example, when the head is placed below
the level of the heart for a long time during a surgical procedure, tissue pressure
from swelling and back-pressure from
pooling of blood (venous pressure)
diminishes the heart’s ability to oxygenate the tissues of the head, including the
optic nerves.
Patient positioning. During multi-level spinal surgery, the patient is typically placed face down. In this position,
the patient’s abdomen is pushed in, putting pressure on the diaphragm and lungs
and causing decreased ventilation.9
